It is known that an optical fibre is a dielectric structure, generally cylindrical in shape with a circular crosssection, which is intended to convey a luminous wave and which is formed by two coaxial media: a central medium with a high refractive index known as the "core" and a peripheral medium known as the "cladding". The diameter of the core varies between a few microns and about 100 microns, depending upon the type of propagation adopted in the fibre. In cases where optical fibres are used in optical telecommunications, it is often considered preferable, in order to increase mechanical flexibility and to guard against the dangers of breakages, to replace a single fibre by an assemblage or "bundle" of identical fibres a few tens of microns in diameter, so that all the fibres of one and the same bundle convey the same information. In very general terms, these bundles comprise a number N of fibres: 7, 19, 37 . . . corresponding to the general formula N = 1 + 3 n (n - 1), so as to enable the fibres to be assembled in the form of a regular hexagon. The fibre or the bundle are disposed in a "protective sheath", generally made of a flexible plastics material.
In order to obtain a detachable connector between a single fibre or a bundle of fibres and either a transmitter or a receiver or a single fibre or another bundle of fibres, it is essential to gather the ends of the fibres, which are extremely fragile, in a terminal which affords them mechanical protection and which is intended to form part of an optical connector that enables the bundle of fibres to be rapidly plugged in and unplugged. In order to minimise the luminous losses caused by the connection, this terminal has to satisfy various requirements. In particular:
IT HAS TO CENTRE THE FIBRE OR THE BUNDLE OF FIBRES WITH MAXIMUM PRECISION SO THAT THE POSITIONING OF THE TERMINAL RELATIVE TO THE CONNECTING MEMBER OF THE ELEMENT TO BE CONNECTED ENABLES THE BUNDLE TO BE POSITIONED IPSO-FACTO RELATIVE TO THE ELEMENT;
IN THE CASE OF A BUNDLE, IT HAS TO GATHER THE ENDS OF THE FIBRES INTO AS COMPACT AN ASSEMBLAGE AS POSSIBLE SO AS TO REDUCE THE INTERSTICES BETWEEN FIBRES AND HENCE TO INCREASE THE RATIO BETWEEN THE USEFUL SURFACE AREA AND THE TOTAL SURFACE AREA OF THE ORIFICE OF THE BUNDLE.
In addition, when the detachable connector is used for assembling two bundles of identical fibres together, it is desirable that the two terminals be designed in such a way that they enable the orifices of each of the fibres to be automatically disposed opposite one another, because a direct coupling device such as this is more efficient than indirect coupling devices, such as lenses or single mixing fibres, where that part of the luminous flux which impinges in the interstices between fibres of the receiving bundle is inevitably lost.